Tool-Selection

Carbide is the standard for gun drilling, but it is not always the best choice. In specific applications — high-silicon aluminum, hardened steels, and abrasive composites — PCD and CBN gun drills can outlast carbide by 10-50x. The catch is that these tools are expensive, brittle, and require a rigid setup. Here is what I have learned about when they work and when they do not. What PCD and CBN Are PCD (polycrystalline diamond) and CBN (cubic boron nitride) are superhard materials. PCD is the second-hardest known material after natural diamond. CBN is the second-hardest after PCD. ...

A gun drill specification sheet can look intimidating the first time you see one. There are diameters, angles, lengths, and tolerances — and each number affects how the drill performs. I have ordered hundreds of gun drills. Here is how I read a spec sheet. Tip Diameter: The Number That Determines Hole Size The tip diameter is the most important number on the sheet. It determines the finished hole size. But the tip diameter is not exactly the hole size — there is an oversize allowance built in. ...

I have a process I use for every new gun drilling job. It starts with the bore print and works through diameter, shank, length, tip geometry, and coating in that order. Skip any of these steps and you risk a tool that wanders, breaks, or wears out before it reaches depth. Here is my full sizing and selection process, along with the reference tables I keep pinned above my bench. ...

I select BTA drill heads based on the material and tolerance requirements. After running BTA drills on thousands of parts across carbon steel, stainless, and superalloys, I have settled on a selection system that covers 90% of what comes through the shop. BTA drill heads come in four main types, each with specific diameter ranges and applications. Pick the wrong head and you will fight chip evacuation, poor surface finish, and short tool life. Pick the right one and the hole drills itself. ...

I use carbide for production and HSS for prototypes. That rule of thumb has served me well across hundreds of jobs, but the real answer depends on material, volume, hole geometry, and your shop’s tolerance for risk. Gun drills are made from either carbide or high-speed steel. Each has distinct advantages, and picking the wrong one costs time and broken tools. Here is what I have learned from running both in production. ...

I use single lip drills for most work and double lip for high production. The choice between these two gun drill types depends on the application requirements, the material being drilled, and the production volume. Here is a detailed comparison of single lip vs double lip gun drills based on my experience. Single Lip Gun Drills Single lip gun drills have one cutting edge and one chip flute. Coolant is delivered through a single hole in the tip. The single cutting edge is supported by guide pads that bear against the bore wall and keep the drill tracking straight. ...